1. Field of the Invention
This invention relates to an apparatus for forming objects from lengths of bar stock and, in particular, to stock feed tube assemblies for supporting and guiding bar stock to manual or automatic turning and forming machinery such as turret lathes, screw machines and the like.
2. Description of the Prior Art
Feed tubes that employ means for reducing sound level output from the tube as a result of rotating bar stock striking the inside surfaces of the tube are known. First attempts involved the use of inserts of flat metallic ribbons helically wound to define longitudinally-extending guide surfaces within the interior of the tube. Examples of such constructions are shown in U.S. Pat. Nos. 1,891,290 to Tessky, 1,904,329 to Rich, and 2,534,811 to Corlett. Lately, governmental pressures for improved working conditions have provided the impetus for seeking stock feed tubes having still greater reductions in noise output levels.
Suggestions have been made to use feed tubes comprised of anechoic polymeric materials -- for example, polyamides and polyethylene. It should be realized that with most metal-turning machines, the stock is rotated at fairly high speeds which, on occasion, may reach speeds as high as 5,000 r.p.m. Under these conditions, if an insufficient running clearance is provided, a significant amount of heat may be developed as a result of the friction forces generated between the stock and the interior guide and support surface of the anechoic feed tube. This condition can result in localized melting of the polymeric liner or severe abrasion or peening of the feed tube that shortens the useful life of the feed tube. Thus, to provide for an acceptable life span, a running clearance is provided between the interior diameter of the feed tube and the peripheral surfaces of the stock being machined to accomodate kinks, bends and other irregularities that commonly occur in metal bar stock. However, if the clearance between the stock and the inner surface of the feed tube is too great, the stock can bend and whip within the feed tube. This results in undue scoring and peening of the liner that also will shorten the life of the liner. The whipping of the stock within the feed tube becomes more intense as the feed stock is consumed and shortened in length since the interior of the tube no longer supports the bar stock to the same axial extent.
One answer to the whipping problem has been the use of feed tubes having liners with inside diameters sufficiently closely related to the stock size so that whipping of the stock is minimized. However, this solution requires a substantial investment by the machine shop operator in several sets of feed tubes of different sizes to process stock of various sizes. Moreover, the change-over to feed tubes of a different size involves additional machine downtime and raises costs.
In previous designs, it has been common to retain the synthetic polymeric feed tubes in outer metallic reinforcing jackets by rivets which extend through the jacket and the feed tube. This is disadvantageous because the rivets score the feed stock and this results in undesirable defacement of the finished products. Also, such systems make replacement of the feed tubes difficult because the rivets must be destructively removed before a new feed tube can be placed within the reinforcing jacket.
Other designs have employed retaining rings that extend into end portions of the reinforcing jacket. These retaining rings are conventionally of a hard metal and are secured by various means such as welding, swaging or riveting. In these designs, replacement of the synthetic polymeric feed tube is difficult because one of the retaining rings must be broken free of the reinforcing jacket to enable the old feed tube to be removed. Further, these designs do not include a means for limiting axial movement of the feed tube assemblies in their supporting structure, such as conventional reels.